We have demonstrated a high incorporation level of H3-choline and C14-choline into the malachite green stainable lipid of spermatozoan and male reproductive tract tissues. Fine structure autoradiographic and biochemical studies are now in progress to investigate the mode of synthesis, storage and secretion of malachite green "affinity lipid" in the male reproductive tract and accessory glands of the rabbit. Labeled spermatozoa are being studied under capacitating conditions to ascertain the significance of this material in the fertilization process.